Homopolymers, unsaturated Polypropylene

General resistance of several generic plastics to oxidation is shown in Table 15.1. LDPE is the least resistant and polypropylene homopolymer is the most resistant, whereas HDPE takes an intermediate place. Resistance of unsaturated C=C aliphatic polymers is quite low because of the ease of abstraction of hydrogen atom. 

High density (HDPE), 52 Irregularities, 52 Linear low density (LLDPE), 52 Low density (LDPE), 52 Molecular weight, 52 Melt flow index, 53 Melting temperature, 51 Moisture absorption, 51 Polymeric forms, 52 Resistance to chemicals, 52 Resistance to oxidation, 52 Shrinkage, 54 Unsaturations, 54 a-transition, 51 P-transition, 51 y-transition, 51 Polyisocyanate, 79 Polylactic acid, 79, 91 Polymer alloys, 48 Polymer processing additives, 646 Polymer rheology, 619 Polymeric forms, 52 Polyphase PlOO, 451 polypropylene (PP), 2, 11 Polypropylene homopolymer, 70... 

These are polymers formed from a single monomer. An example is polyethene (polyethylene), which is made by polymerization of ethene (CH2 CH2). Typically such polymers are formed by addition reactions involving unsaturated molecules. Other similar examples are polypropene (polypropylene), polystyrene, and polytetrafluoroethene (PTFE). Homopolymers may also be made by condensation reactions (as in the case of polyurethane). 

ESR spectroscopy has been applied to studies of unsaturation and other structural features in a wide range of homopolymers including polyethylene [101-110], polypropylene [111-121], polybutenes [115], polystyrene [122-124], PVC [125,126], polyvinylidene chloride [127], polymethylmethacrylate [128-137], polyethylene glycol polycarbonates [137-140], polyacrylic acid [136-139, 141, 142], polyphenylenes [143], polyphenylene oxides [143], polybutadiene [144], conjugated dienes [145,146], polyester resins [146], cellophane [143,147] and also to various copolymers including styrene grafted polypropylene [148], ethylene-acroline [149], butadiene-isobutylene [150], vinyl acetate copolymers [151] and vinyl chloride-propylene. 

Polypropylene (PP) is another common plastic used extensively in packaging apphca-tions. Its homopolymer is produced by catalytic addition polymerization of propylene. In the case of PP copolymer, a co-monomer such as ethylene is also used. An organo-metallic catalyst is used, which attaches to propylene, works as functional group and reacts with the unsaturated bond of propylene (or with other co-monomer in case of copolymerization) to form a long chain polymer (Maier and Calafirt, 1998). 

Graft copolymers of a,j3-unsaturated carboxylic acids and anhydrides on a polypropylene backbone have often been used as compatibilizers for PP/PA blends. For example, a PP grafted with glycidyl and styrene moieties is a suitable compatibilizer (49). Likewise, a propylene homopolymer backbone is grafted with a st50-ene/meth-acrylic acid copolymer (PP-g-(S/MAA)) (50). 

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